The invention relates to an apparatus for providing relative angular adjustment between a crankshaft and at least one camshaft and wherein the camshaft is positively connected through a drive-end flange shaft to a cylindrical hollow shaft via an actuating element. The hollow shaft surrounds the actuating element and has a driving wheel connected to the drive shaft. The actuating element divides an annular space formed between the hollow shaft and flange shaft into two separate working spaces and is alternatingly supplied with oil pressure from the engine oil circuit and returned again to it, as a function of the position of a control element located in the flange shaft.
An apparatus for altering the phasing between a main shaft and a control shaft in engines which has two separate control shafts for inlet valves and outlet valves and which allows changing between two different control time settings is known from German Offenlegungsschrift 3,126,620. Each of two control time settings corresponds to an end position of a movable drive member which is connected via couplings, of which at least one is provided with a helical gearing, to a main shaft and a control shaft. Through axial displacement, a rotation of the control shaft relative to the main shaft is obtained. The adjustment of the drive member into one of two end positions is performed by the pretension of a spring. The adjustment into the other end position is caused by pressure oil from the engine oil circuit. A slide valve operated by centrifugal force assumes three different positions, depending on the engine speed. It accordingly opens and closes oil outflow bores and thus controls the oil pressure on the drive member. In a position of the slide valve which opens an oil outflow bore when the engine is below a certain engine speed, only a spring force, which holds the drive member in an end position, acts on the drive member.
If the engine speed exceeds this first threshold speed value, the slide valve closes the oil outflow bore on account of the change in centrifugal force and the drive member is displaced by the increasing engine oil pressure against spring tension, axially into a second end position. A relative turning thus occurs between the main shaft and control shaft and a control time setting adapted to this engine operating state is thus achieved as a result. After exceeding a further threshold value for the engine speed, the slide valve is moved into a position which again makes an oil outflow possible. Due to the spring force, the drive member is again returned into its first end position, with corresponding relative rotation. The adjustment of the drive member when the threshold values for the engine speed are not reached also takes place in the same way.
German Offenlegungsschrift 3,316,162 also shows a comparable apparatus, the only difference being that the operation of the drive member is not controlled by centrifugal forces, instead the slide valve controlling the oil flow is electromagnetically operable.
Both said apparatuses have the disadvantage that the control is performed by means of an influencing of the oil outflow. In one of the two working positions of the drive member there is a constant oil flow, with the associated losses.
A further disadvantage is that in a resetting operation into the initial position, the oil, forced out of the working space by the spring force from the drive member, has to be taken away through the same oil outflow bore through which the oil constantly flowing in this position of the slide valve is also passed. This fact results in an undesired slowing of the resetting operation.
At low engine speeds, for example in idling operation, the oil pressure is too low to be able to bring about an adjustment. For this reason, the drive member must be brought into the position corresponding to this operating state by spring force. At low speed and consequently also low oil pressure, such a spring force can prevent an adjustment of the drive member by pressure oil in the time periods in which there is an inhibiting camshaft torque, so that an adjustment can only take place when there is a driving camshaft torque, that is to say intermittently. In order to avoid the undesired resetting of the drive member caused by the spring force together with the camshaft torque, the helical gearing must be of a self-inhibiting design, that is with flat angle of skew. However, such an angle of skew also only allows for a short adjustment distance, i.e. the relative angular adjustment between main shaft and control shaft or camshaft is small, and thus so too is the influence of a control time alteration.
The object of the invention is to create an apparatus of the generic type, avoiding the disadvantages mentioned, which in a compact and with a simple construction that ensures a rapid and reliable angular adjustment.
The object is achieved in that the actuating element is designed as a rocker which is mounted pivotably on the flange shaft about a pivot axis running parallel to the camshaft axis and is in engagement with the hollow shaft. The rocker is able to assume two end positions in the annular space between the hollow shaft and flange shaft.
A further advantage is obtained by having a spring element, provided in a hollow space of the rocker surrounding the flange shaft, to hold the rocker under pretension in its respective end position. The spring element can consist of a spring clip embracing the flange shaft for over more than half the circumferential length of this shaft and the spring element also bears on at least two points on the inside on the rocker. The two end positions of the rocker are defined by two stop edges on the hollow shaft for limiting the pivoting movement of the rocker. The rocker can also be held in each end position at the respective stop by a resilient detent element thereat. The rocker engages with a nose in a gate fitted on the inside of the hollow shaft. The flange shaft has a transverse bore which connects the control element, arranged inside the flange shaft, to the hollow space of the rocker.
The sprocket wheel carrier is designed as hollow shaft. A sprocket wheel is located thereon and is driven by a crankshaft via a chain connection. The open side of the sprocket wheel carrier is closed by the camshaft, which is firmly connected to a hollow flange shaft running coaxially to the sprocket wheel carrier axis.
The sprocket wheel carrier, camshaft and flange shaft together form an annular hollow space, which is subdivided into two working spaces by an actuating element, which is designed as a rotary vane and is mounted pivotably between two end positions about an axis running parallel to the camshaft. In the hollow flange shaft there is arranged a control plunger, which has two working positions. The plunger is held by a spring in one of these working positions and can be moved axially against the spring force into the other working position by an armature of an electromagnet fixed in the engine, firmly connected to it. Depending on the armature position, the supply of pressure oil from the engine oil circuit is fed via an oil bore of the camshaft into one of the working spaces and the outflow of oil from the respective other working space is returned to the engine. The rotary vane is adjusted hydraulically in both directions and therefore does not require a separate spring force for the return. Thus, no spring force has to be overcome in the adjustment and consequently a greater actuating torque can be realized. The elimination of the spring thus also allows an adjustment in the low speed range, that is at only low engine oil pressure. In contrast to German Offenlegungsschrift 3,126,620, defining the generic type, there is also no constant oil flow. Instead oil flow occurs only during an adjusting operation until one of the two working positions has been reached.
In the basic position, the electromagnet is de-energized and the control plunger is held by the spring in the one end position. After switching on of the electromagnet, the control plunger is moved against the spring force into the other end position. Due to the resultant supplying of pressure oil into one of the two working spaces, the rotary vane is pivoted and rotates the flange shaft via a support connection of a nose fitted on a gate provided on the inside of the hollow shaft bearing of the driving wheel. This also rotates the camshaft relative to the sprocket wheel driven by the crankshaft. Due to the axial pivoting of the rotary vane, oil is pushed out from the respectively other working space and returned to the engine oil circuit. When the electromagnet is switched off, the control plunger returns with the aid of the spring force into its initial position. This causes a supply of pressure oil to the other working space and releases the oil outflow from the previously pressurized working space. By this renewed actuating operation, the previously performed relative rotation is reversed again.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.